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WASHINGTON (AP) - Federal health officials say they still have safety concerns about an experimental diet pill from drugmaker Vivus Inc., as the company prepares to make a second attempt to convince experts of the drug’s safety next week.

Vivus, based in Mountain View, Calif., is one of three small drugmakers racing to bring the first new prescription weight loss drug to market in more than a decade. In the past two years the Food and Drug Administration has rejected pills from all three: Arena Pharmaceuticals Inc., Orexigen Therapeutics Inc. and Vivus. All three companies are in the process of resubmitting their products.

The FDA had rejected the diet pill Qnexa in October 2010. Vivus has resubmitted the drug with additional follow-up information, hoping for a more favorable ruling.

But in documents posted online Friday, the FDA reiterated concerns about two safety issues that plagued the pill the time first around: Potential heart problems and birth defects in women who become pregnant while taking the drug.

On Wednesday the FDA will ask experts at a public meeting to weigh in on those issues, specifically risks of cleft lip defects associated with one of the ingredients in Qnexa. The experts will also discuss increased blood pressure and higher heart rates reported for patients taking the drug.

The panel of doctors will take a final vote on whether the drug appears safe and effective. The group’s recommendation is not binding, and the FDA is expected to make its final decision in April.

With U.S. obesity rates nearing 35 percent among adults, doctors and public health officials say new weight-loss therapies are desperately needed. And even a modestly effective drug could have blockbuster potential. But none of the three medicines before the FDA represents a breakthrough in research.

Qnexa is a combination of two older drugs. The amphetamine phentermine, which is approved for short-term weight loss, and topiramate, an anticonvulsant drug sold by Johnson & Johnson as Topamax. Phentermine helps suppress appetite, while topiramate is supposed to make patients feel more satiated.

Many analysts had picked Qnexa as the most promising contender of the new potential diet pills because of the high level of weight loss reported in company studies. On average, patients lost more than 10 percent of their total body mass.

But at Qnexa’s first FDA panel in 2010, experts assembled by the food and drug regulator voted 10-6 to not recommend the drug’s approval. Panelists said the drug was associated with a number of dangerous side effects, including suicidal thoughts, heart palpitations, memory lapses and birth defects.

On Wednesday Vivus will offer to conduct a follow-up study to monitor patients for any heart problems, if Qnexa is approved. Experts will consider whether the company should be required to conduct that study before FDA gives approval. The company will also offer a plan to make sure women who are likely to become pregnant do not use the drug. One of the two ingredients in Qnexa, topirimate, is known to more than double the risk of birth defects.

Qnexa’s other ingredient, phentermine, was one half of the dangerous fen-phen combination, a weight loss treatment pushed by doctors that was never approved by the FDA. The regimen was linked to heart-valve damage and lung problems in the late 1990s, and the FDA forced drugmaker Wyeth to withdraw two versions of its drug fenfluramine.

Currently there is just one prescription drug on the market for long-term weight loss: Roche’s Xenical, which is not widely used because of modest weight loss results.